In June 2024, scientists detected a mysterious, powerful burst of radio waves originating from within our galaxy. At first, they thought it was coming from a pulsar or another undiscovered cosmic object. However, an analysis revealed the origin of the signal was too close to the Earth. Astronomers think it was caused by a long-dead NASA satellite Relay 2, was launched in 1964 but ceased operations in 1967 after its communication systems failed. Yet, nearly 60 years later, it mysteriously emitted a powerful radio signal, the researchers said in a new preprint study, which was posted June 13 to the server arXiv and has not yet been peer-reviewed.

Relay 2: A Silent Satellite Sends a Loud Signal

According to the study, the signal was detected using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope array. These intense flashes typically originate from deep space and can carry more energy in milliseconds than the sun emits over several days.

But this signal, lasting just 30 nanoseconds, was traced back to the vicinity of Earth, too close for ASKAP to focus on clearly. After ruling out cosmic sources, the team traced the pulse to the orbit of Relay 2. Despite having no functioning systems, the satellite somehow emitted the brightest radio flash in the sky at that moment.

Researchers proposed two theories: a micrometeorite impact that created a radio-emitting plasma cloud, or an electrostatic discharge (ESD) caused by charge buildup on the satellite’s aging materials.

New Clues About Spacecraft Behavior and Space Debris

Though both mechanisms could produce similar signals, scientists lean toward electrostatic discharge as the likelier cause. According to space physicists, older spacecraft like Relay 2 may be especially prone to such energy releases due to outdated materials and limited shielding.

Karen Aplin told New Scientist that studying these accidental emissions could help monitor ESD events on today’s small satellites — many of which also lack advanced protection. In an increasingly crowded orbital environment, this detection method may offer a novel tool for evaluating space debris and satellite health.